Brexit could end up going down as one of the biggest and most needless self-inflicted wounds in history, Hillary Clinton told an audience in Belfast on Wednesday.

Speaking at Queen’s University, the 2016 Democratic presidential candidate said to loud applause: “I make no excuse for being against Brexit from the start. I thought it was a bad idea before the referendum and I think it is an even worse idea now. It may well go down as one of greatest and most unnecessary self-inflicted wounds in modern history.”

She added: “Brexit seems to be going ahead one way or the other. It is crucial that however it comes out, Brexit should not be allowed to undermine the peace and prosperity that has been so dearly won here.” Clinton urged the region’s two main communities to put aside their differences to form a temporary executive to provide a unified voice on Brexit. The Northern Ireland assembly has not sat since it collapsed in January last year.

Clinton, who was at the university to receive an honorary degree, warned that “the uncertainty surrounding Brexit for everyone is substantial, but here in Northern Ireland is acute”, saying the country was both “a contributor to the impasse and compelling reason to resolve it”.

She accepted that the politics of coalition-building were tough, but said the current stakes went beyond politics, stressing that a functioning Northern Ireland executive weighing in on the final terms of the negotiations could have an impact.

She added that it would also send a clear message to businesses already skittish about Brexit that Northern Ireland remained open for business.